Thermal processing furnaces, also known as diffusion furnaces, have been widely known and used for many years to perform a variety of semiconductor fabrication processes, including annealing, diffusion, oxidation, and chemical vapor deposition (CVD). As a result, these processes are well understood, especially with regard to the impact of process variables on the quality and uniformity of resulting products.
Thermal processing furnaces typically employ either a horizontal-type furnace, or a vertical-type furnace. For some applications, vertical-type furnaces are preferred because they create less particles during use, thus decreasing the incidence of contamination and wafer waste. In addition, they can be easily automated, and they require less floor space because of their relatively small footprint.
Both conventional types of diffusion furnaces are designed to heat semiconductor wafers to desired temperatures to promote either diffusion of the dopants to a desired depth while maintaining line width smaller than 1 micron, as known, or to perform other conventional processing techniques such as the application of an oxide layer to the wafer or deposition of a chemical vapor layer to the wafer. The heating requirements of the wafer during processing are known and well understood, and thus are closely monitored.
Conventional vertical-type thermal processing furnaces are designed to support the outer tube and inner tube within the furnace in the vertical position. The inner tube is conventionally referred to as a liner, and typical liners include silicon carbide liners which operate above 500° Celsius, such as in the TEL a-303i Vertical Nitride Furnace. Although the silicon carbide liners are designed to operate at temperatures above 500° Celsius, the current fixtures provided by manufactures for replacing the silicon carbide liners are designed for use at room temperature. Unfortunately, to achieve room temperatures the entire furnace must be inactivated and cooled, which is an exceptionally expensive process. Every time a furnace is brought offline to room temperature, numerous expensive parts need to be serviced and/or replaced before the vertical furnace can be heated again and brought back online. For instance, the inner thermalcouple (TC) needs to be replaced as it is usually contaminated with a nitride film which degrades operational properties and necessitates requalification. This part alone may cost $7,000.00, excluding labor. In addition, a stainless steel manifold and O ring needs to be replaced, which is usually contaminated with ammonia chloride. A fair estimate for bringing a vertical furnace offline and then again back online, such as to replace the silicon carbide liner may cost in excess of $30,000.00
A silicon carbide liner will eventually generate particles in excess of a maximum allowable particle count after a predetermined time, such as a thickness of 3.5 microns, and needs to be replaced. However, the entire furnace does not need to be retrofitted as often, but is conventionally brought offline to provide for the replacement of the silicon carbide liner since the removal fixtures are only designed by the manufacture to operate at room temperature.
Accordingly, there is a need to provide for the retrofitting of a silicon carbide liner within an operating heated vertical furnace, including the installation and removal of the liner from the operating heated semiconductor vertical furnace without causing damage to either the old or new liner, or the furnace itself. Such a solution would significantly reduce the overall operating cost of the vertical furnace by allowing the retrofitting of the silicon carbide liner itself without bringing the furnace offline.